Device for artificial respiration with an endotracheal tube

ABSTRACT

A device for ventilation, comprising
         a ventilator for providing a stream of gas for ventilation at an outlet,   a hose for inspiration air one end of which is connected to the outlet,   a double-lumen endotracheal tube one lumen of which, at its end distal to the patient, is connected to the other end of the hose for inspiration air,   flow meters for measuring the streams of gas in the two lumina of the endotracheal tube,   pressometers for measuring the pressures at the ends distal to the patient of the two lumina,   an evaluation means for determining the flow resistance in a lumen flowed through by gas because of the stream of gas measured therein and the pressures measured, and   a means for outputting an information about the flow resistance of the lumina.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not Applicable

BACKGROUND OF THE INVENTION

The invention relates to a device for ventilation via an endotrachealtube.

The predominant majority of patients being ventilated during anintensive-care therapy or anaesthesia have their airway secured by anendotracheal tube. To this end, an endotracheal tube which consists of aplastic or rubber tube, as a rule, is introduced into the tracheathrough the mouth or nose or by a making an incision in the trachea(“tracheotomy”). At the tracheal end, the endotracheal tube mostly isprovided with a inflatable endotracheal tube “cuff” which seals thetrachea, permits ventilation at an excess pressure, and protects theairways from the penetration of foreign matter. The end distal to thepatient of the endotracheal tube is coupled to a ventilation device viaa hose system. At the point of transition from the endotracheal tube tothe hose system, there is an Y connection piece which has connectedthereto an inspiratory hose and an expiratory hose or expiratory valveleading to the atmosphere.

A respiratory air filter can be disposed between the endotracheal tubeand the hose system to minimize the exchange of micro-organisms andother contaminants between the patient and hose system. The extension oftime intervals between the exchanges of the hose which becomes possiblethereby is advantageous both economically and ecologically. Further,heat-and-moisture exchangers may be provided between the hose system andthe endotracheal tube which cause the inspiration air to be humidifiedto prevent the patient's airways from becoming parched. This isaccomplished by condensing the moisture contained in the expiration airon specific filter-like materials and re-evaporating the moisture duringthe succeeding inspiration. Further, there is a so-called “activehumidification” via a heated evaporator in the inspiratory hose of thehose system.

The lungs effect an exchange of gas with the external air in a pendularprocess. At this stage, whenever an inspiration takes place gas whichhas been left behind from prior expiration in the so-called “dead space”first gets into the lungs. The dead space is the entirety of all airconductors which are flowed through during both inspiration andexpiration. It comprises the bronchi and trachea as well as theconventionally single-lumen endotracheal tube and any precedingbreathing air filters or heat-to-moisture exchangers. It ends in anY-connector which ramifies the airway for inspiration and expiration.

The respiratory excursions subject the lungs to mechanical loads andrequire the spontaneously breathing patient to do breathing effort.Since the dead space (both anatomical and device-related) can constitutea significant percentage of the respiratory stroke (about 30% to morethan 50%) its minimization is an important step towards reducing suchloads and breathing effort fractions. A known action to reduce the deadspace is to insert an endotracheal tube having two lumina (a“double-lumen endotracheal tube”) which are separately connected to theinspiratory hose and expiratory hose or the expiratory valve leading tothe atmosphere. A ventilation system having a double-lumen endotrachealtube is described in DE 25 35 191 A1, for example. In a double-lumenendotracheal tube, a separator for the inspiration and expiration legsof the ventilation device is installed in lieu of a connection piece forthe two lumina. It is located deeply in the trachea at the tracheal endof the endotracheal tube. Accordingly, this reduces the dead space ofthe system and the breathing effort which caused by the dead space.

Another advantage of double-lumen endotracheal tubes is provided whenthere is a pressure-regulating ventilation. During such a ventilation,the ventilator aims at regulating the pressure at the Y connectionpiece. To this end, the common ventilators do not carry out a pressuretap which is separately led up to the Y connection piece because thepressure prevailing there can be measured just as well via the uprightgas column of the hose which is just not flowed through during therespective respiratory phase. When a double-lumen endotracheal tube isused the Y connection piece and, hence, the regulation point will beshifted into the trachea. As a direct consequence, the patient need nolonger overcome that part of breathing effort which is caused by theflow resistances in a single-lumen endotracheal tube. The task ofovercoming the flow resistances of the double-lumen endotracheal tube isautomatically imposed on the ventilator.

When the endotracheal tube kinks or foreign matter such as secretionsfrom the trachea settle(s) in its interior its resistance will increase.This can cause a hazard to the patient because it will impede itsventilation and/or high pressures will build up in the lungs (withrestriction being preponderant to expiration). Since such changes occurto the portion of the endotracheal tube that cannot be seen in a visualinspection only late signs will be noticed, i.e. reductions toventilation or pressure rises.

These disadvantages can be overcome to a limited extent by monitoringthe pressure at the Y connection piece and the gas flows. However, suchmonitoring cannot discriminate or associate the mechanical properties ofthe structures beyond the Y connection piece (filter, endotracheal tube,airways, lungs, surrounding tissue, muscle activity). Therefore,monitoring the tube properties is only possible to a very limited extentand only major changes are detected, if at all.

Another problem is posed by the necessity for constant humidification ofthe patient's inspiration air because the endotracheal tube keeps itaway from the natural humidifiers (the mucosae of the nose and pharynx).Heat-and-moisture exchangers, as a rule, simultaneously function asfilters, thus forming a contaminant barrier between the patient and thehose system. However, they require to be alternately flowed through byexpiration and inspiration air to satisfy their function. Therefore,they cannot be employed for double-lumen endotracheal tubes. At present,if double-lumen endotracheal tubes are used it is only possible toactively humidify such air by means of electrically heated evaporators.

Another problem is how to remove secretions and foreign matter from theendotracheal tube. While a ventilation therapy is performed the naturalcleaning mechanism of the airways is capable of transporting secretionsand foreign matter into the trachea up to the endotracheal tube, if atall. They have to be drawn off not later than from this point. To thisend, it is usual to disconnect the Y connection piece from theendotracheal tube so permit a suction catheter to be introduced into theendotracheal tube. This interrupts ventilation and any continuouslypositive airway pressure (CPAP) or positive end-expiratory pressure(PEEP), which is a common prophylaxis against the collapse of diseasedparts of the lung, cannot be maintained. Therefore, special inflationmanoeuvres become necessary after this suction to re-open collapsedparts of the lungs.

Furthermore, it has been known already to introduce the suction catheterthrough a particular angled adapter, which forms a seal around thecatheter, between the endotracheal tube and the Y connection piece. Theventilator remains connected to the endotracheal tube and ventilationcan be continued, on a principle. However, problems will arise by thefact that the portion of the lumen that is responsible for ventilationis reduced in dependence on the dimensions of the endotracheal tube andsuction catheter and, as a consequence, its resistance to bothinspiration and expiration air is more or less increased. Recent studieshave shown that continuing a volume-controlled ventilation should beavoided in any case under these circumstances: Hazardous positive ornegative pressures are possible, which depend on the pattern ofventilation and the different dimensions of the hose. Therefore, ifventilation is to be continued under a suction this has definitely to bedone in a pressure-regulated mode. Even then, if a conventionalsingle-lumen endotracheal tube is used the pressure in the trachea willalways be distinctly below the target pressure setting during a suctionbecause there is the endotracheal tube with its reduced lumen betweenthe trachea and the Y connection piece, the point of measurement andregulation.

DE 195 28 113 A discloses a ventilation device for the controlledmechanical ventilation of patients including a measurement andevaluation of the expiratory time constant of the respiratory system.Characteristic changes of the time constant-to-volume relationship aresupposed to allow the detection and differentiation of elevatedresistances or obstructions of the endotracheal tube, on one hand, andthose of the trachea and bronchi, on the other.

GB 2 318 518 discloses a double-lumen endotracheal tube in which onelumen serves for the supply of a continuous flow of fresh gas and thelarger lumen serves for discontinuous expiration. Controlled ventilationis effected by a phased closure of the larger lumen. The expiration limbof the device has connected thereto a pressure sensor.

U.S. Pat. No. 3,102,537 A discloses a respiration device with a facemask, particularly for air and space travel, which ensures improvedtransfer of moisture from the expired air to the inspired air and amaximum saving of oxygen or another inspired gas from an externalsource. A common wall permeable to moisture is disposed between theexpiration and the inspiration air conduit. In addition, there is areservoir which is passed in by a first portion of the expired gas inorder to be inspired first during the following inspiration.

BRIEF SUMMARY OF THE INVENTION

Accordingly, it is the object of the invention to provide an operativelyimproved device for ventilation via an endotracheal tube.

The object is achieved by a device for ventilation having

-   -   a ventilator for providing a stream of gas for respiration at an        outlet,    -   a hose for inspiration air one end of which is connected to the        outlet,    -   a double-lumen endotracheal tube one lumen of which is distally        connected to the other end of the inspiratory hose,    -   flow meters connected to the ends distal to the patient of the        two lumina for measuring the streams of gas in the two lumina of        the endotracheal tube,    -   pressometers connected to the ends distal to the patients of the        two lumina for measuring the pressures at the ends distal to the        patient of the two lumina,    -   an evaluation means for determining the flow resistance in a        lumen which is flowed through by gas on the basis of the stream        of gas measured therein and the pressures measured, and    -   a means to output an information about the flow resistance of        the lumina.

The invention relies on the possibility of determining the flowresistance in the lumen which is flowed through by gas from the valuesmeasured for the stream of gas resistance in the lumen which is flowedthrough by gas and the pressures prevailing at the two lumina. Namely,the pressometer connected to the end distal to the patient of the lumenwhich is flowed through by gas measures the pressure directly at the enddistal to the patient of this lumen and the pressometer connected to theend distal to the patient of the lumen which is not flowed through bygas measures the pressure at the tracheal end of the lumen which isflowed through so that the pressure loss of the lumen which is flowedthrough results from the two pressures. Then, the flow resistance of thelumen which is flowed through can be calculated, along with the streamof gas passing through the lumen which is flowed through. For thispurpose, reference is made to the interconnections known from the fluidmechanics between the pressure loss, volumetric flow, and flowresistance coefficient of tubes which are flowed through. The flowresistance, in turn, allows to directly conclude therefrom whether theendotracheal tube is inadmissibly kinked or clogged so that correctiveactions are required. In a software-controlled device for ventilation,the evaluation and display procedures described can be easilyimplemented under a software control.

The rule for all of the inventive devices for ventilation is that thelumen for expiration may be connected to the atmosphere via a valve,preferably an actively controlled valve, or may be connected to an inletof the ventilator for expired breathing air via an expiratory hose. Theformer may be the case particularly for emergency ventilators. It iscommon specifically for anaesthesia ventilation that the expired air isreturned to the ventilator if gases which are relatively expensive arefed to the ventilation system and a recovery of the gases from theventilation system is beneficial.

The flow meters and/or pressometers can be located on the ventilatorand/or at the end of the tracheal tube. Preferably, they are on theventilator because if they were disposed at the end of the tracheal tubethey would make it more difficult to handle them. If the expiratory endof the endotracheal tube is not connected to the ventilator via anexpiratory hose it is obligatory to arrange the flow meter andpressometer of the expiratory end on the endotracheal tube. Also in suchcase, however, it is preferred to locate the flow meter and pressometerof the inspiratory end in the ventilator.

Basically, the device determines the flow resistance of the lumen whichis flowed through by gas and the hose connected thereto towards theventilator. If the properties of the hose with no endotracheal tube areknown to the device it can determine the flow resistance of theendotracheal tube. For a determination of the properties of the hose, itcan be disconnected from the endotracheal tube and can be opened to theatmosphere or two hoses can be connected to each other and be flowedthrough by streams of gas. If the hose is opened to the atmosphere thepressure loss can be determined by means of the ambient pressure, whichis known, and the pressure measured at one hose end and the stream ofgas which was measured. When the hoses are connected to each other thepressures measured at the ends of the hoses are incorporated into thecalculation. Preferably, there are valve means between the endotrachealtube and the hose/hoses to connect the hose/hoses to the environmentand/or to each other.

An embodiment of the device has

-   -   an endotracheal tube and    -   at least one membrane permeable to water in a wall between two        lumina of the endotracheal tube and/or between two hoses for        connecting the endotracheal tube to a ventilator.

The moisture from the expired air condenses on the side of thewater-permeable membrane that forms part of the expiration air limb inorder to be re-absorbed by the dry inspired air on the other side of themembrane that forms part of the limb for inspiration air. Since theexchange of moisture takes place in a counter-current it can becomehighly effective if suitable dimensions are chosen. Efficiency can beimproved by heating the stream of gas in the limb for inspiration airbecause warm gas will take up moisture more rapidly and better.Likewise, it is possible to enhance efficiency by using a membranematerial which preferably transports water from the expiratory limb tothe inspiratory limb. Such “asymmetric” materials are known to be usedin sanitary products (sanitary towels or baby's diapers), for example. Alarge exchange surface can also be achieved by causing the hoses and/orlumina of a double-lumen endotracheal tube to envelope each other, e.g.by surrounding each other concentrically.

It can also be beneficial to combine the second solution with the firstsolution. This also applies to any aspects of the first and secondsolutions.

According to an aspect, the device for ventilation has

-   -   a ventilator for providing a stream of gas for ventilation at an        outlet,    -   a hose for inspiration air one end of which is connected to the        outlet,    -   a double-lumen endotracheal tube one lumen of which is distally        connected to the other end of the inspiratory hose,    -   pressometers for measuring pressures at the ends of the two        lumina distal from the patient,    -   a closable opening at the distal end of the lumen for the        expired stream of gas to sealingly introduce a suction catheter        up to the tracheal end of this lumen, and    -   a means for regulating the pressure to a predetermined value in        the lumen which is not flowed through by the gas.

Pressure-regulated ventilation via the double-lumen endotracheal tubemay re readily continued under a suction with no positive or negativepressures occurring because the ventilation pressure is regulated justin the place where suction also makes itself felt, i.e. in the trachea.The means for pressure regulation is connected to the pressometers andcontrols the stream of gas. The ventilation pressure can further becontrolled by a valve at the end distal to the patient of the lumen forexpiration. The control of the pressure via the stream of gaspresupposes that the inspiratory limb of the device, i.e. the hose andthe lumen via which the stream of gas is fed for ventilation, does notexert too much resistance to the flow to prevent the ventilation devicefrom building up the desired pressure in the trachea. Introduction ofthe suction catheter into the lumen through which the expiratory air isdischarged avoids a disadvantageous increase in flow resistance in theother lumen.

It is preferred to additionally design the lumen for the expired streamof gas with a larger cross-section than has the lumen for the stream ofgas für ventilation (asymmetric double-lumen endotracheal tube). Thearrangement of the suction catheter could result in a reduction ofexpiration; however, this effect is alleviated or eliminated by thesuction stream of gas which also causes some sort of expiration (passingby the ventilator). The pressure range predetermined by the user is notexited at any time in any case. For the first time, this allows to carryout a ventilation therapy during which the pressure never drops belowthe predetermined CPAP or PEEP (see above), even in connection withsuction manoeuvres.

According to an aspect, the device for ventilation has

-   -   a ventilator to provide a stream of gas for ventilation at an        outlet,    -   a hose for inspiration gas one end of which is connected to the        outlet,    -   a double-lumen endotracheal tube one lumen of which is connected        to the other end of the hose for inspiration gas at the end        distal to the patient, and    -   a device for applying an oscillating pressure to the end distal        to the patient of the endotracheal tube lumen connected to the        hose for inspiration air.

Applying a high-frequency pressure oscillation to the inspiratory limbof the ventilator improves the exchange of gas with the patient. Thisallows to reduce the stream of gas for patient ventilation. In thiscontext, “high-frequency” denotes frequencies which exceed the breathingfrequency of the patients, particularly frequencies which amount to atleast more than 5 Hz. The application of a high-frequency pressureoscillation has admittedly been known in connection with single-lumenendotracheal tubes. However, since the dead volume is considerablepressure fluctuations of a high energy have to be applied here toachieve an improvement to gas exchange. The provision of suitableoscillators poses a problem. When used in conjunction with adouble-lumen endotracheal tube, an improvement to gas exchange isachieved already by means of oscillators which exhibit relatively lowenergies and amplitudes because the dead volume is reduced very much.The propagation of pressure fluctuations into the lungs can be enhancedby configuring the lumen for expiration as a low pass type for pressureoscillation. Preferably, the expiratory limb of the ventilation devicecontains an active valve the actuation of which is coordinated with theoscillation of the pressure generator.

BRIEF DESCRIPTION OF THE DRAWING

The invention will be described below with reference to the accompanyingdrawing which schematically shows an embodiment.

FIG. 1 is a schematic of an embodiment of the invention.

FIG. 2 is a schematic showing the flowmeters and pressometers, housed inventilator 1, and also showing the computer, connected to the flowmetersand pressometers.

DETAILED DESCRIPTION OF THE INVENTION

While this invention may be embodied in many different forms, there aredescribed in detail herein a specific preferred embodiment of theinvention. This description is an exemplification of the principles ofthe invention and is not intended to limit the invention to theparticular embodiment illustrated.

The device for ventilation comprises a ventilator 1 with an outlet 2 atwhich a stream of gas is provided and an inlet 3 to which a stream ofexpired gas can be fed. At the inlet 3, the ventilator 1 has an activevalve which is closed during inspiration in order to maintain thepressure in the lungs, and which is opened during expiration. Behind thevalve, the expired gas can be released to the environment.Alternatively, the stream of expired gas can be prepared for reuse inthe ventilator 1 (by removing the CO₂) and the gas needed forventilation will be re-supplied to the outlet where fresh ventilationgas can be admixed.

Further, there is an endotracheal tube 4 which has two lumina 5, 6. Atits tracheal end, this double-lumen endotracheal tube 4 has aninflatable cuff 7 which provides a seal towards a trachea 8, theendotracheal tube 4 being advanced up to a point just in front of thebronchi 9.

The ventilator 1 is connected to the end distal to the patient of theendotracheal tube 4 via a hose system 10. The hose system 10 has aninspiratory hose 11 which is connected to the outlet 2 and lumen 5. Itfurther has an hose 12 for expiratory gas which is connected to thelumen 6 and inlet 3.

The ventilator 1 houses flow meters for measuring the streams of gasfrom the outlet 2 and into the inlet 3. The ventilator I also housespressometers for measuring the pressure at the outlet 2 and inlet 3.

Using the aid of the gas flow and pressure values, a computer integratedin the ventilator calculates the flow resistance each in the lumens 5and 6 which are just flowed through by gas. If admissible limit valuesare exceeded the endotracheal tube 4 is assumed to be kinked or cloggedand an optical or acoustic signal is emitted.

Furthermore, the wall between the two lumina 5, 6 is designed as amembrane 13 which is permeable to water in an area. This membrane 13causes moisture to be transmitted from the expiration air in the lumen 6to the inspiration air in lumen 5.

Furthermore, the lumen 6 is closed by an opening 14 through which asuction catheter can be sealingly introduced, if required, up to thetracheal end of the endotracheal tube 4. Since the pressure is measuredat the outlet 2 and inlet 3 and the streams of gas are regulated in theventilator 1 the effect is that the pressure in the trachea ismaintained at a constant level.

Finally, a means for generating a, pulsating pressure which has afrequency exceeding the breathing frequency can be disposed in theventilator 1 and acts upon the outlet 2 to intensify the exchange of gasduring ventilation.

FIG. 2 schematically shows flowmeter 20 and pressometer 22, both shownin phantom, which are connected to outlet 2. Flowmeter 24 andpressometers 26, both shown in phantom, are connected to inlet 3. Theflowmeters 20 and 24, and pressometers 22 and 26 are all connected to acomputer 28, which determines the flow resistance in the lumens 5 and 6.The flowmeters 20 and 24 measure the gas flow in lumens 5 and 6, whilethe pressometers 22 and 26 measure the pressure in lumens 5 and 6.

The above disclosure is intended to be illustrative and not exhaustive.This description will suggest many variations and alternatives to one ofordinary skill in this art. All these alternatives and variations areintended to be included within the scope of the claims where the term“comprising” means “including, but not limited to”. Those familiar withthe art may recognize other equivalents to the specific embodimentsdescribed herein which equivalents are also intended to be encompassedby the claims.

Further, the particular features presented in the dependent claims canbe combined with each other in other manners within the scope of theinvention such that the invention should be recognized as alsospecifically directed to other embodiments having any other possiblecombination of the features of the dependent claims. For instance, forpurposes of claim publication, any dependent claim which follows shouldbe taken as alternatively written in a multiple dependent form from allprior claims which possess all antecedents referenced in such dependentclaim if such multiple dependent format is an accepted format within thejurisdiction (e.g. each claim depending directly from claim 1 should bealternatively taken as depending from all previous claims). Injurisdictions where multiple dependent claim formats are restricted, thefollowing dependent claims should each be also taken as alternativelywritten in each singly dependent claim format which creates a dependencyfrom a prior antecedent-possessing claim other than the specific claimlisted in such dependent claim below.

This completes the description of the preferred and alternateembodiments of the invention. Those skilled in the art may recognizeother equivalents to the specific embodiment described herein whichequivalents are intended to be encompassed by the claims attachedhereto.

The invention claimed is:
 1. A device for ventilation of a patient, thedevice comprising a ventilator having an outlet for providing a streamof gas for ventilation and an inlet for receiving a stream of expiredgas, a double-lumen endotracheal tube having an end distal to thepatient and a tracheal end that engages the patient's trachea, wherein,at the end distal to the patient, a lumen for inspiratory gas isconnected to the ventilator outlet and a separate lumen for expiratorygas is connected to the ventilator inlet such that, during ventilation,a stream of gas is only flowing through one lumen at a time, a flowmeter located at the end of the double-lumen endotracheal tube distal tothe patient and connected to the inspiratory lumen and a separate flowmeter located at the end of the double-lumen endotracheal tube distal tothe patient and connected to the expiratory lumen, and a pressometerlocated at the end of the double-lumen endotracheal tube distal to thepatient and connected to the inspiratory lumen and a separatepressometer located at the end of the double-lumen endotracheal tubedistal to the patient and connected to the expiratory lumen, thepressometers being adapted for alternating between measuring thepressure directly at the end distal to the patient of the double-lumenendotracheal tube and the pressure at the tracheal end of thedouble-lumen endotracheal tube depending upon which lumen through whichgas is flowing.
 2. The device according to claim 1 wherein one or moreof the flow meters or pressometers are integrated in the ventilator. 3.The device according to claim 1 comprising valve means located at theventilator inlet for connecting the with one or both of the environmentand the outlet.
 4. The device according to claim 1, further comprising aclosable opening at the end distal to the patient of the expiratorylumen to sealingly introduce a suction catheter up to the tracheal endof the endotracheal tube.
 5. The device according to claim 1, furthercomprising a means for applying a high frequency oscillating pressure tothe end distal to the patient of the inspiratory lumen.
 6. The deviceaccording to claim 1, further comprising a computer for determining theflow resistance in the inspiratory lumen and the expiratory lumen, basedon measurements from the flow meters and the pressometers.
 7. The deviceaccording to claim 1, further comprising an evaluation means fordetermining the flow resistance in an individual lumen.
 8. The deviceaccording to claim 1, further comprising a means for outputting aninformation about the flow resistance of the lumina.
 9. The deviceaccording to claim 1, further comprising at least one membrane permeableto water in a wall between the inspiratory lumen and the expiratorylumen of the endotracheal tube.
 10. The device according to claim 9,wherein the membrane passes water from the expired breath in theexpiratory lumen to the inspiratory lumen.
 11. The device according toclaim 9, further comprising means for heating the stream of ventilationgas.
 12. The device according to claim 9, wherein the membrane comprisesa filter.
 13. The device according to claim 1, wherein the endotrachealtube comprises an asymmetric endotracheal tube.
 14. The device accordingto claim 13, wherein the expiratory lumen has a larger cross-sectionthan the inspiratory.
 15. The device according to claim 1, wherein onelumen of the endotracheal tube is enveloped by the other lumen of theendotracheal tube.
 16. A method for determining the flow resistance ofan endotracheal tube comprising: (a) providing a ventilation systemcomprising: (i) a ventilator having an outlet for providing a stream ofgas for ventilation and an inlet to which a stream of expired gas isfed; (ii) a double-lumen endotracheal tube having an end distal to thepatient and a tracheal end that engages the patient's trachea, wherein,at the end distal to the patient, a lumen for inspiratory gas isconnected to the ventilator outlet and a separate lumen for expiratorygas is connected to the ventilator inlet such that, during ventilation,a stream of gas is only flowing through one lumen at a time; (iii) aflow meter located at the end of the double-lumen endotracheal tubedistal to the patient and connected to the inspiratory lumen and aseparate flow meter located at the end of the double-lumen endotrachealtube distal to the patient and connected to the expiratory lumen; and(iv) a pressometer located at the end of the double-lumen endotrachealtube distal to the patient and connected to the inspiratory lumen and aseparate pressometer located at the end of the double-lumen endotrachealtube distal to the patient and connected to the expiratory lumen, thepressometers being adapted to alternate between measuring the pressuredirectly at the end distal to the patient of the double-lumenendotracheal tube and the pressure at the tracheal end of thedouble-lumen endotracheal tube depending upon which lumen through whichgas is flowing; (b) calculating the flow of gas in one or both lumina;(c) calculating the pressure of the gas in one or both lumina; and (d)determining the flow resistance within the endotracheal tube based onthe calculated gas flow and gas pressure.
 17. The method of claim 16,wherein one or more of the flow meters and pressometers are located onthe ventilator.
 18. The method of claim 16, wherein the device furthercomprises evaluation means for determining the flow resistance withinthe endotracheal tube.
 19. A method for increasing moisture content inair inspired by a patient through an endotracheal tube, the methodcomprising: (a) providing a ventilation system comprising: (i) aventilator having an outlet for providing a stream of gas forventilation; (ii) a double-lumen endotracheal tube, having aninspiratory lumen for transmission of the gas for ventilation from theventilator and a separate expiratory lumen for transmission of airexpired by the patient, the inspiratory lumen and the expiratory lumenbeing separated by a wall; and (iii) at least one membrane permeable towater located in the wall between the inspiratory lumen and theexpiratory lumen of the endotracheal tube; and (b) initiatinginspiration and expiration of air through the endotracheal tube suchthat moisture from the expired air condenses on the side of the membraneadjacent the expiratory lumen, the moisture exchanges through themembrane, and is re-absorbed in the inspiratory lumen by the stream ofgas for ventilation provided by the ventilator.
 20. The method of claim19, further comprising heating the stream of gas in the inspiratorylumen.
 21. The method of claim 19, wherein one lumen of the endotrachealtube is enveloped by the other lumen of the endotracheal tube.
 22. Amethod of removing clogging matter from an endotracheal tube duringintubation of a patient while maintaining tracheal pressure, the methodcomprising: (a) providing a ventilation system comprising: (i) aventilator having an outlet for providing a stream of gas forventilation and an inlet for receiving a stream of expired gas; (ii) adouble-lumen endotracheal tube, having an end distal to the patient anda tracheal end that engages the patient's trachea, wherein, as the enddistal to the patient, a lumen for inspiratory gas is connected to theventilator outlet and a separate lumen for expiratory gas is connectedto the ventilator inlet such that, during ventilation, a stream of gasis only flowing through one lumen at a time; (iii) a closable opening inthe expiratory lumen; (iv) a flow meter located at the end of theendotracheal tube distal to the patient and connected to the inspiratorylumen and a separate flow meter located at the end of the endotrachealtube distal to the patient and connected to the expiratory lumen; (v) apressometer located at the end of the endotracheal tube distal to thepatient and connected to the inspiratory lumen and a separatepressometer located at the end of the endotracheal tube distal to thepatient and connected to the expiratory lumen, the pressometers beingadapted to alternate between measuring the pressure directly at the enddistal to the patient of the endotracheal tube and the pressure at thetracheal end of the endotracheal tube depending upon which lumen throughwhich gas is flowing; and (vi) evaluation means for determining the flowresistance in a lumen in relation to the gas flow and the gas pressureof the lumen; (b) sealingly introducing through the closable opening adevice for removal of clogging matter in the expiratory lumen; (c)removing the clogging matter from the expiratory lumen; and (d)maintaining and regulating tracheal pressure by continuously evaluatinggas flow and gas pressure and continuously increasing or decreasing thestream of gas provided by the ventilator to compensate for pressurechanges arising from said removal of the clogging matter.
 23. The methodof claim 22, wherein step (d) comprises using the pressometer connectedto the lumen through which gas is flowing to measure the gas pressuredirectly at the end distal to the patient of the lumen through which gasis flowing and using the pressometer connected to the lumen throughwhich gas is not flowing to measure the gas pressure at the tracheal endof the lumen through which gas is flowing.
 24. The method of claim 16,wherein step (c) comprises using the pressometer connected to the lumenthrough which gas is flowing to measure the gas pressure directly at theend distal to the patient of the lumen through which gas is flowing andusing the pressometer connected to the lumen through which gas is notflowing to measure the gas pressure at the tracheal end of the lumenthrough which gas is flowing.
 25. The method of claim 24, comprisingusing the gas pressure directly at the end distal to the patient of thelumen through which gas is flowing and the gas pressure at the trachealend of the lumen through which gas is flowing to calculate the pressureloss of the lumen through which gas is flowing.
 26. The method of claim16, comprising alternating between determining flow resistance of theinspiratory lumen and the expiratory lumen of the double-lumenendotracheal tube.
 27. The method of claim 16, comprising using thedetermined flow resistance to evaluate whether the endotracheal tube iskinked or clogged and whether corrective actions are required.